Golf ball

ABSTRACT

In a golf ball having a core, a cover and a coating layer, the coating layer is formed of a urethane coating that includes an organic solvent having a boiling point of 80° C. or less, a silicone-based additive and, as a curing agent, a polyisocyanate which contains an adduct and an isocyanurate of hexamethylene diisocyanate. Although the golf ball includes a silicone-based additive in the outer surface (coating layer) of the ball, it has a good spin performance on approach shots not only when wet but also when normally dry, and is capable of exhibiting both a good water-repelling performance and a good friction performance.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2021-102359 filed in Japan on Jun. 21,2021, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to golf ball having a core, a cover and acoating layer. The invention relates more particularly to a golf ball inwhich the cover is formed of a polyurethane resin composition and thecoating layer is made of a urethane coating composition.

BACKGROUND ART

A coating composition is often applied to the surface portion of a golfball in order to protect the ball surface or maintain an attractiveappearance. Such golf ball coating compositions are preferably two-partcurable polyurethane coatings prepared by mixing together a polyol and apolyisocyanate just prior to use, in part because such coatings are ableto withstand large deformation, impacts and friction.

JP-A 2014-524335 describes a golf ball which incorporates a “low-energy”composition as a soft surface coating. This low-energy composition,which lowers the coefficient of friction and is easy to handle duringproduction, is applied in order to, for example, lower the tendency ofmud to stick to the ball. A silicone-based additive is described asbeing used in the low-energy composition.

JP-A 2019-10190 discloses that imparting water repellency to the surfaceof a golf ball lowers the friction coefficient of the golf ball surface,preventing a drop in the distance traveled by the ball on driver shotswhen the ball is played in rainy weather. Examples of water-repellingadditives mentioned therein include silicone-based additives such assilicone resins, silicone fluids and silicone rubbers.

In addition, JP-A 2021-53367 teaches that by forming the outer surfacelayer of a material having a contact angle of 90° or more, the surfaceof a golf ball becomes water-repelling and the friction coefficient ofthe golf ball surface decreases, making it possible to prevent a drop inthe distance traveled by the ball on driver shots when played in rainyweather. Examples of water-repelling additives mentioned therein includesilicone-based additives such as silicone resins, silicone fluids andsilicone rubbers.

However, with the use of a silicone-based additive in these prior-artgolf balls, although a water-repelling performance is obtained and thespin performance when the ball is wet rises, when the ball is dry as isnormally the case, the spin rate on approach shots tends to decrease.

For this reason, JP-A 2021-53367 discloses that the outer surface layerof the golf ball is formed of a material which includes awater-repelling additive and hexamethylene diisocyanate (HMDI), andmoreover that this HMDI includes an adduct and an isocyanurate thereof.However, even this golf ball is unable to provide a fully satisfactoryspin performance on approach shots.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a golfball which, although it includes a silicone-based additive in the outersurface (coating layer) of the ball, has a good spin performance onapproach shots not only when wet but also when normally dry, and canexhibit both a good water-repelling performance and a good frictionperformance.

We have discovered that, in a urethane coating composition which formsthe coating layer normally serving as the outer surface portion of agolf ball, certain desirable effects can be achieved by including as thecuring agent a polyisocyanate which includes an adduct and anisocyanurate of hexamethylene diisocyanate (HMDI), and by alsoselecting, as an organic solvent that can be used in the base resin orthe curing agent, a relatively low-boiling solvent. Namely, when thecomposition is prepared such that the organic solvent in the surfaceportion of the applied film (coat) evaporates before the siliconeingredient rises to the outer surface during application and curing ofthe coating composition takes place, achieving both a goodwater-repelling performance and a good friction performance is possible,giving the ball a good spin performance on approach shots not only whenwet, but also when normally dry. In particular, by using alow-resilience urethane resin composition as the golf ball covermaterial, the controllability on approach shots is improved even more,enabling the object of the invention to be fully achieved.

Accordingly, the present invention provides a golf ball having a core, acover and a coating layer, wherein the coating layer is formed of aurethane coating that includes an organic solvent having a boiling pointof 80° C. or less, a silicone-based additive and, as a curing agent, apolyisocyanate which includes an adduct and an isocyanurate ofhexamethylene diisocyanate (HMDI).

In a preferred embodiment of the golf ball of the invention, the organicsolvent having a boiling point of 80° C. or less is included in aproportion, based on the overall amount of the coating composition, ofat least 20 wt %.

In another preferred embodiment of the inventive golf ball, the mixingratio by weight (A)/(B) between the isocyanurate (A) and the adduct (B)of hexamethylene diisocyanate is from 85/15 to 15/85.

In yet another preferred embodiment, at least one layer of the cover isformed of a resin composition composed of (I) a polyurethane or apolyurea and (II) aromatic vinyl elastomer, which aromatic vinylelastomer has a Shore D hardness of 30 or less and a rebound resilienceof 30% or less. In this embodiment, the content of component (II) may befrom 5 to 20 parts by weight per 100 parts by weight of component (I).The resin composition in the same embodiment may further include (III) athermoplastic polyester elastomer having a Shore D hardness of 45 orless, a rebound resilience of 74% or less, and a melt viscosity at 200°C. and a shear rate of 243 sec⁻¹ of 1.5×10⁴ dPa·s or less. In stillanother preferred embodiment, when the ball is allowed to fall freelyonto an impact surface inclined 58° to the horizontal from a heightposition 3 m above the surface, the amount of sliding by the ball,designated as “Ds” and defined as the perpendicular displacement by theball from where sliding of the ball on the impact surface begins towhere sliding ends, is 2.0 mm or less, and the contact time of the ballafter sliding, designated as “Tc” and defined as the time from whensliding of the ball on the impact surface ends until the ball separatesfrom the impact surface, is at least 400 μs.

Advantageous Effects of the Invention

The golf ball of the invention, even when a silicone-based additive isincluded in the outer surface (coating layer) of the ball, has a goodspin rate on approach shots not only when wet but also when normallydry, and is capable of exhibiting both a good water-repellingperformance and a good friction performance.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The objects, features and advantages of the invention will become moreapparent from the following detailed description.

The golf ball of the invention is a golf ball having a core, a cover anda coating layer.

The core may be formed using a known rubber material as the basematerial. A known base rubber such as natural rubber or synthetic rubbermay be used as the base rubber. More specifically, it is recommendedthat polybutadiene, especially cis-1,4-polybutadiene having a cisstructure content of at least 40%, be chiefly used. If desired, naturalrubber, polyisoprene rubber, styrene-butadiene rubber or the like may beused together with the foregoing polybutadiene in the base rubber.

The polybutadiene may be synthesized with a metal catalyst, such as aneodymium or other rare-earth catalyst, a cobalt catalyst or a nickelcatalyst.

Co-crosslinking agents such as unsaturated carboxylic acids and metalsalts thereof, inorganic fillers such as zinc oxide, barium sulfate andcalcium carbonate, and organic peroxides such as dicumyl peroxide and1,1-bis(t-butylperoxy)cyclohexane may be included in the base rubber. Ifnecessary, commercial antioxidants and the like may be suitably added.

The core may be produced by vulcanizing/curing the rubber compositioncontaining the above ingredients. For example, production may be carriedout by kneading the composition using a mixer such as a Banbury mixer ora roll mill, compression molding or injection molding the kneadedcomposition using a core mold, and curing the molded body by suitablyheating it at a temperature sufficient for the organic peroxide and theco-crosslinking agent to act, i.e., between 100° C. and 200° C.,preferably between 140° C. and 180° C., for a period of 10 to 40minutes.

In the golf ball of the invention, the core is encased with a cover ofone layer or a plurality of layers. Such a golf ball is exemplified bygolf balls having a core and a one-layer cover, and golf balls having acore, an intermediate layer encasing the core and an outermost layerencasing the intermediate layer.

In this invention, the resin material making up at least one layer ofthe cover is formed of a resin composition containing components (I) and(II) below:

-   -   (I) a polyurethane or a polyurea, and    -   (II) an aromatic vinyl elastomer.

(I) Polyurethane or Polyurea

The polyurethane or polyurea is a substance that is capable of servingas the base resin of the above cover material (resin composition). Thepolyurethane (I-a) and polyurea (I-b) which may be used as thiscomponent are described in detail below.

(I-a) Polyurethane

The polyurethane has a structure which includes soft segments composedof a polymeric polyol (polymeric glycol) that is a long-chain polyol,and hard segments composed of a chain extender and a polyisocyanate.Here, the polymeric polyol serving as a starting material may be anythat has hitherto been used in the art relating to polyurethanematerials, and is not particularly limited. It is exemplified bypolyester polyols, polyether polyols, polycarbonate polyols, polyesterpolycarbonate polyols, polyolefin polyols, conjugated dienepolymer-based polyols, castor oil-based polyols, silicone-based polyolsand vinyl polymer-based polyols. Specific examples of polyester polyolsthat may be used include adipate-type polyols such as polyethyleneadipate glycol, polypropylene adipate glycol, polybutadiene adipateglycol and polyhexamethylene adipate glycol; and lactone-type polyolssuch as polycaprolactone polyol. Examples of polyether polyols includepoly(ethylene glycol), poly(propylene glycol), poly(tetramethyleneglycol) and poly(methyltetramethylene glycol). These polyols may be usedsingly, or two or more may be used in combination.

It is preferable to use a polyether polyol as the polymeric polyol.

The long-chain polyol has a number-average molecular weight that ispreferably in the range of 1,000 to 5,000. By using a long-chain polyolhaving a number-average molecular weight in this range, golf balls madewith a polyurethane composition that have excellent properties,including a good rebound and good productivity, can be reliablyobtained. The number-average molecular weight of the long-chain polyolis more preferably in the range of 1,500 to 4,000, and even morepreferably in the range of 1,700 to 3,500.

Here and below, “number-average molecular weight” refers to thenumber-average molecular weight calculated based on the hydroxyl valuemeasured in accordance with JIS-K1557.

The chain extender is not particularly limited; any chain extender thathas hitherto been employed in the art relating to polyurethanes may besuitably used. In this invention, low-molecular-weight compounds with amolecular weight of 2,000 or less which have on the molecule two or moreactive hydrogen atoms capable of reacting with isocyanate groups may beused. Of these, preferred use can be made of aliphatic diols having from2 to 12 carbon atoms. Specific examples include 1,4-butylene glycol,1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol and2,2-dimethyl-1,3-propanediol. The use of 1,4-butylene glycol isespecially preferred.

Any polyisocyanate hitherto employed in the art relating topolyurethanes may be suitably used without particular limitation as thepolyisocyanate. For example, use can be made of one or more selectedfrom the group consisting of 4,4′-diphenylmethane diisocyanate,2,4-toluene diisocyanate, 2,6-toluene diisocyanate, p-phenylenediisocyanate, xylylene diisocyanate, 1,5-naphthylene diisocyanate,tetramethylxylene diisocyanate, hydrogenated xylylene diisocyanate,dicyclohexylmethane diisocyanate, tetramethylene diisocyanate,hexamethylene diisocyanate, isophorone diisocyanate, norbornenediisocyanate, trimethylhexamethylene diisocyanate,1,4-bis(isocyanatomethyl)cyclohexane and dimer acid diisocyanate.However, depending on the type of isocyanate, crosslinking reactionsduring injection molding may be difficult to control.

The ratio of active hydrogen atoms to isocyanate groups in thepolyurethane-forming reaction may be suitably adjusted within apreferred range. Specifically, in preparing a polyurethane by reactingthe above long-chain polyol, polyisocyanate and chain extender, it ispreferable to use the respective components in proportions such that theamount of isocyanate groups included in the polyisocyanate per mole ofactive hydrogen atoms on the long-chain polyol and the chain extender isfrom 0.95 to 1.05 moles.

The method of preparing the polyurethane is not particularly limited.Preparation using the long-chain polyol, chain extender andpolyisocyanate may be carried out by either a prepolymer process or aone-shot process via a known urethane-forming reaction. Of these, meltpolymerization in the substantial absence of solvent is preferred.Production by continuous melt polymerization using a multiple screwextruder is especially preferred.

It is preferable to use a thermoplastic polyurethane material as thepolyurethane, with an ether-based thermoplastic polyurethane materialbeing especially preferred. The thermoplastic polyurethane material usedmay be a commercial product, illustrative examples of which includethose available under the trade name Pandex® from DIC Covestro Polymer,Ltd., and those available under the trade name Resamine fromDainichiseika Color & Chemicals Mfg. Co., Ltd.

(I-b) Polyurea

The polyurea is a resin composition composed primarily of urea linkagesformed by reacting (i) an isocyanate with (ii) an amine-terminatedcompound. This resin composition is described in detail below.

(i) Isocyanate

The isocyanate is not particularly limited. Any isocyanate used in theprior art relating to polyurethanes may be suitably used here. Use maybe made of isocyanates similar to those mentioned above in connectionwith the polyurethane material.

(ii) Amine-Terminated Compound

An amine-terminated compound is a compound having an amino group at theend of the molecular chain. In this invention, the long-chain polyaminesand/or amine curing agents shown below may be used.

The long-chain polyamine is an amine compound which has on the moleculeat least two amino groups capable of reacting with isocyanate groups andwhich has a number-average molecular weight of from 1,000 to 5,000. Inthis invention, the number-average molecular weight is more preferablyfrom 1,500 to 4,000, and even more preferably from 1,900 to 3,000.Examples of such long-chain polyamines include, but are not limited to,amine-terminated hydrocarbons, amine-terminated polyethers,amine-terminated polyesters, amine-terminated polycarbonates,amine-terminated polycaprolactones, and mixtures thereof. Theselong-chain polyamines may be used singly, or two or more may be used incombination.

The amine curing agent is an amine compound which has on the molecule atleast two amino groups capable of reacting with isocyanate groups andwhich has a number-average molecular weight of less than 1,000. In thisinvention, the number-average molecular weight is more preferably lessthan 800, and even more preferably less than 600. Specific examples ofsuch amine curing agents include, but are not limited to,ethylenediamine, hexamethylenediamine, 1-methyl-2,6-cyclohexyldiamine,tetrahydroxypropylene ethylenediamine, 2,2,4- and2,4,4-trimethyl-1,6-hexanediamine,4,4′-bis(sec-butylamino)dicyclohexylmethane,1,4-bis(sec-butylamino)cyclohexane, 1,2-bis(sec-butylamino)cyclohexane,derivatives of 4,4′-bis(sec-butylamino)dicyclohexylmethane,4,4′-dicyclohexylmethanediamine, 1,4-cyclohexane-bis(methylamine),1,3-cyclohexane-bis(methylamine), diethylene glycol di(aminopropyl)ether, 2-methylpentamethylenediamine, diaminocyclohexane,diethylenetriamine, triethylenetetramine, tetraethylenepentamine,propylenediamine, 1,3-diaminopropane, dimethylaminopropylamine,diethylaminopropylamine, dipropylenetriamine, imidobis(propylamine),monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine,diisopropanolamine, isophoronediamine,4,4′-methylenebis(2-chloroaniline), 3,5-dimethylthio-2,4-toluenediamine,3,5-dimethylthio-2,6-toluenediamine, 3,5-diethylthio-2,4-toluenediamine,3,5-diethylthio-2,6-toluenediamine,4,4′-bis(sec-butylamino)diphenylmethane and derivatives thereof,1,4-bis(sec-butylamino)benzene, 1,2-bis(sec-butylamino)benzene,

N,N′-dialkylaminodiphenylmethane,N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine, trimethylene glycoldi-p-aminobenzoate, polytetramethylene oxide di-p-aminobenzoate,4,4′-methylenebis(3-chloro-2,6-diethyleneaniline),4,4′-methylenebis(2,6-diethylaniline), m-phenylenediamine,p-phenylenediamine and mixtures thereof. These amine curing agents maybe used singly or two or more may be used in combination.

(iii) Polyol

Although not an essential ingredient, in addition to above components(i) and (ii), a polyol may also be included in the polyurea. The polyolis not particularly limited, but is preferably one that has hithertobeen used in the art relating to polyurethanes. Specific examplesinclude the long-chain polyols and/or polyol curing agents mentionedbelow.

The long-chain polyol may be any that has hitherto been used in the artrelating to polyurethanes. Examples include, but are not limited to,polyester polyols, polyether polyols, polycarbonate polyols, polyesterpolycarbonate polyols, polyolefin-based polyols, conjugated dienepolymer-based polyols, castor oil-based polyols, silicone-based polyolsand vinyl polymer-based polyols. These long-chain polyols may be usedsingly or two or more may be used in combination.

The long-chain polyol has a number-average molecular weight ofpreferably from 1,000 to 5,000, and more preferably from 1,700 to 3,500.In this number-average molecular weight range, an even better resilienceand productivity are obtained.

The polyol curing agent is preferably one that has hitherto been used inthe art relating to polyurethanes, but is not subject to any particularlimitation. In this invention, use may be made of a low-molecular-weightcompound having on the molecule at least two active hydrogen atomscapable of reacting with isocyanate groups and having a molecular weightof less than 1,000. Of these, the use of aliphatic diols having from 2to 12 carbon atoms is preferred. Specific examples include 1,4-butyleneglycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol and2,2-dimethyl-1,3-propanediol. The use of 1,4-butylene glycol isespecially preferred. The polyol curing agent has a number-averagemolecular weight of preferably less than 800, and more preferably lessthan 600.

A known method may be used to produce the polyurea. A prepolymerprocess, a one-shot process or some other known method may be suitablyselected for this purpose.

Component (I) has a material hardness on the Shore D hardness scalewhich, from the standpoint of the spin properties and scuff resistanceachieved by the golf ball, is preferably 52 or less, more preferably 50or less, and even more preferably 48 or less. From the standpoint of themoldability, the lower limit in the material hardness on the Shore Dscale is preferably at least 38, and more preferably at least 40.

Component (I) has a rebound resilience which, from the standpoint ofenhancing the spin rate on approach shots, is preferably at least 55%,more preferably at least 57%, and even more preferably at least 59%. Therebound resilience is measured in accordance with JIS-K 6255: 2013.

Component (I) serves as the base resin of the resin composition. Tofully impart the scuff resistance of the urethane resin, it accounts forat least 50 wt %, preferably at least 60 wt %, more preferably at least70 wt %, even more preferably at least 80 wt %, and most preferably atleast 90 wt %, of the resin composition.

(II) Aromatic Vinyl Elastomer

Next, the aromatic vinyl elastomer (II) is described.

By including the aromatic vinyl elastomer (II) in, as subsequentlydescribed, a small amount at or below a given level, the compatibilitywith above component (I) serving as the base resin is good, thecompatibility with the subsequently described thermoplastic polyesterelastomer serving as component (III) is good, and a good scuffresistance and moldability can be maintained in a golf ball and themethod of manufacture thereof.

The aromatic vinyl elastomer is a polymer (elastomer) composed ofpolymer blocks made up primarily of an aromatic vinyl compound, andrandom copolymer blocks made up of an aromatic vinyl compound and aconjugated diene compound. That is, the aromatic vinyl elastomergenerally has, as exemplified by SEBS, blocks made up of an aromaticvinyl compound component that are located at both ends of the polymerand serve as hard segments, and intermediate blocks made up of aconjugated diene compound component that are located between the endsand serve as soft segments. Polymers in which an aromatic vinyl-basedcomponent has been randomly introduced into the conjugated dienecompound component that makes up the intermediate blocks have also beenreported in recent research. The hardness of the aromatic vinylelastomer generally becomes lower as the content of the aromatic vinylthat forms the hard segments decreases; at the same time, because theamount of the soft segment component increases, the rebound resiliencerises. On the other hand, in cases where an aromatic vinyl component israndomly introduced into the soft segments serving as the intermediateblocks, the rebound resilience decreases with little if any rise in thehardness. A similar effect can be obtained by using a conjugated dienecompound having a high glass transition temperature (Tg) in place of thearomatic vinyl compound that is randomly introduced into theintermediate blocks. In the present invention, to fully exhibit theworking effects described above, it is particularly desirable to use theabove polymer (elastomer) in a hydrogenated form.

Examples of the aromatic vinyl compound in the polymer include styrene,α-methylstyrene, p-methylstyrene, divinylbenzene, 1,1-diphenylethylene,N,N-dimethyl-p-aminoethylstyrene and N,N-diethyl-p-aminoethylstyrene.These may be used singly or two or more may be used together. Of thesearomatic vinyl compounds, styrene is preferred.

Examples of the conjugated diene compound in the polymer includebutadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene,2-methyl-1,3-pentadiene and 1,3-hexadiene. These may be used singly ortwo or more may be used together. Of these compounds, butadiene andisoprene are preferred. Butadiene is more preferred.

Units originating from the above conjugated diene compounds, such asunits originating from butadiene, become ethylene units or butyleneunits when subjected to hydrogenation. For example, when astyrene-butadiene-styrene block copolymer (SBS) is hydrogenated, itbecomes a styrene-ethylene/butylene-styrene block copolymer (SEBS).

As mentioned above, it is preferable for the aromatic vinyl elastomerused as component (II) to be one that has been hydrogenated; i.e., ahydrogenated aromatic vinyl elastomer. The hydrogenated aromatic vinylelastomer is preferably an elastomer obtained by hydrogenating a polymercomposed of polymer blocks made up primarily of an aromatic vinylcompound and random copolymer blocks made up of an aromatic vinylcompound and a conjugated diene compound; and more preferably anelastomer obtained by hydrogenating a polymer composed up of polymerblocks made up primarily of styrene and random copolymer blocks made upof styrene and butadiene. An elastomer obtained by hydrogenating apolymer composed of polymer blocks made up primarily of styrene andrandom copolymer blocks made up of styrene and butadiene, particularly apolymer having at both ends a polymer block made up primarily of styrene(especially one having at each of the two ends a polymer blockconsisting entirely of styrene) and having random copolymer blocks inbetween, is especially preferred. It is thought that a lower hardnessand a lower resilience are both achieved by using a copolymer havingthis structure. In addition, the rate of solidification after molding israpid and so the degree of tack is low. Also, the compatibility with (I)the polyurethane or polyurea serving as the base resin is excellent,enabling decreases in the physical properties owing to such blending tobe held to a minimum.

Illustrative examples of the hydrogenated aromatic vinyl elastomerinclude styrene-ethylene/butylene-styrene block copolymers (SEBS),styrene-isobutylene-styrene block copolymers (SIBS),styrene-isoprene-styrene block copolymers (SIS), styrene-isobutyleneblock copolymers (SIB), styrene-ethylene/propylene-styrene blockcopolymers (SEPS), styrene-ethylene/ethylene/propylene-styrene blockcopolymers (SEEPS), styrene-butadiene/butylene-styrene block copolymers(SBBS) and styrene-ethylene-propylene block copolymers (SEP).

In the aromatic vinyl elastomer, the proportion of the copolymeraccounted for by units originating from the aromatic vinyl compound(i.e., the aromatic vinyl compound content, preferably the styrenecontent) is preferably at least 30 wt %, more preferably at least 40 wt%, even more preferably at least 50 wt %, and most preferably at least60 wt %. By thus setting the aromatic vinyl compound content, preferablythe styrene content, to a high level, the compatibility with thepolyurethane or polyurea serving as component (I) is good and, moreover,the desired hardness and moldability can be prevented from worsening.The content of units from the above aromatic vinyl compound (preferablythe styrene content) can be determined by calculation from H′-NMRmeasurements.

In the aromatic vinyl elastomer, the glass transition temperature (Tg),as indicated by the tan 6 peak temperature obtained by dynamicviscoelasticity measurement with a dynamic mechanical analyzer (DMA), ispreferably from −20 to 50° C., more preferably at least 0° C., and evenmore preferably at least 5° C. The thinking here is that, by having thetan 6 peak temperature be close to the temperature at which the golfball is normally used, the rebound resilience of the overall resincomposition is kept low in the temperature region at which the golf ballis normally used, enabling the desired effects of the invention to beincreased.

A commercial product may be used as the aromatic vinyl elastomer servingas component (II). Examples of such commercial products include thoseavailable under the trade names S.O.E., Tuftec™ and Tufprene™ from AsahiKasei Corporation, and those available under the trade name Dicstyrenefrom DIC Corporation.

Component (II) has a material hardness on the Shore D hardness scalewhich, to increase the spin rate on approach shots, is 30 or less,preferably 28 or less, and more preferably 26 or less. The lower limitis preferably at least 18, and more preferably at least 20.

Component (II) has a rebound resilience which, to maintain the spin rateof the ball on approach shots and keep the ball rebound on approachshots low so as achieve good controllability, is 30% or less, preferably25% or less, and more preferably 22% or less. By thus keeping therebound resilience very low, a small amount of addition will not have anadverse effect on the golf ball properties, enabling a decrease in theball initial velocity on approach shots to be achieved. To minimize thedecrease in rebound and the reduction in distance on shots with adriver, the lower limit of the rebound resilience is preferably at least15%, and more preferably at least 20%. This rebound resilience ismeasured in accordance with JIS-K 6255: 2013.

The content of component (II) per 100 parts by weight of component (I)is preferably 30 parts by weight or less, more preferably 20 parts byweight or less, and even more preferably 15 parts by weight or less. Thelower limit in this content is preferably at least 5 parts by weight,and more preferably at least 10 parts by weight. When the content ofcomponent (II) is too high, the scuff resistance and moldability mayworsen. On the other hand, when the content of component (II) is toolow, the low hardness and the desired rebound resilience as a coverresin material may not be obtained, and the ball initialvelocity-lowering effect on approach shots may diminish.

A thermoplastic polyester elastomer (III) may be additionally includedin the resin composition containing above components (I) and (II).Component (III) is described below.

(III) Thermoplastic Polyester Elastomer

The thermoplastic polyester elastomer (III) is a component which impartsat least a given level of resilience to the resin composition and, alongwith imparting such resilience, enables the ball to maintain a spin rateat or above a given level on approach shots. The thermoplastic polyesterelastomer serving as component (III) has a good compatibility with abovecomponent (I) serving as the base resin, the compatibility being betterthan that of, in particular, hitherto used thermoplastic polyesterelastomers, and so is able to impart the ball with a good scuffresistance. In addition, including the thermoplastic polyester elastomeras an essential ingredient in the resin composition provides at least agiven level of melt viscosity, imparting the resin composition withhardenability after it has been molded. That is, the thermoplasticpolyester elastomer suppresses a decline in the viscosity of the overallresin composition due to the softness of component (I) serving as thebase resin, thus preventing a decrease in moldability (productivity) andan increase in appearance defects in the molded golf balls and alsoholding down a rise in production costs owing to an increased coolingtime.

The thermoplastic polyester elastomer serving as component (III) is aresin composition made up of (III-a) a polyester block copolymer and(III-b) a rigid resin. Component (III-a) is made up of, in turn,(III-a1) a high-melting crystalline polymer segment and (III-a2) alow-melting polymer segment.

The high-melting crystalline polymer segment (III-a1) within thepolyester block copolymer serving as component (III-a) is a polyestermade of one or more compound selected from the group consisting ofaromatic dicarboxylic acids and ester-forming derivatives thereof anddiols and ester-forming derivatives thereof

Illustrative examples of the aromatic dicarboxylic acids includeterephthalic acid, isophthalic acid, phthalic acid,2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid,anthracenedicarboxylic acid, diphenyl-4,4′-dicarboxylic acid,diphenoxyethanedicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid,5-sulfoisophthalic acid and sodium 3-sulfoisophthalate. In thisinvention, an aromatic dicarboxylic acid is primarily used. However,where necessary, some of this aromatic dicarboxylic acid may be replacedwith an alicyclic dicarboxylic acid such as 1,4-cyclohexanedicarboxylicacid, cyclopentanedicarboxylic acid or 4,4′-dicyclohexyldicarboxylicacid or with an aliphatic dicarboxylic acid such as adipic acid,succinic acid, oxalic acid, sebacic acid, dodecanedioic acid or dimeracid. Exemplary ester-forming derivatives of dicarboxylic acids includelower alkyl esters, aryl esters, carboxylic acid esters and acid halidesof the above dicarboxylic acids.

Next, a diol having a molecular weight of 400 or less may be suitablyused as the diol. Specific examples include aliphatic diols such as1,4-butanediol, ethylene glycol, trimethylene glycol, pentamethyleneglycol, hexamethylene glycol, neopentyl glycol and decamethylene glycol;alicyclic diols such as 1,1-cyclohexanedimethanol,1,4-dicyclohexanedimethanol and tricyclodecanedimethanol; and aromaticdiols such as xylylene glycol, bis(p-hydroxy)diphenyl,bis(p-hydroxy)diphenylpropane,2,2′-bis[4-(2-hydroxyethoxy)phenyl]propane,bis[4-(2-hydroxyethoxy)phenyl]sulfone,1,1-bis[4-(2-hydroxyethoxy)phenyl]cyclohexane,4,4′-dihydroxy-p-terphenyl and 4,4′-dihydroxy-p-quaterphenyl. Exemplaryester-forming derivatives of diols include acetylated forms and alkalimetal salts of the above diols.

These aromatic dicarboxylic acids, diols and derivatives thereof may beused singly or two or more may be used together.

In particular, the following may be suitably used as component (III-a1):high-melting crystalline polymer segments composed of polybutyleneterephthalate units derived from terephthalic acid and/or dimethylterephthalate together with 1,4-butanediol; high-melting crystallinepolymer segments composed of polybutylene terephthalate units derivedfrom isophthalic acid and/or dimethyl isophthalate together with1,4-butanediol; and copolymers of both.

The low-melting polymer segment serving as component (III-a2) is analiphatic polyether and/or an aliphatic polyester.

Examples of the aliphatic polyether include poly(ethylene oxide) glycol,poly(propylene oxide) glycol, poly(tetramethylene oxide) glycol,poly(hexamethylene oxide) glycol, copolymers of ethylene oxide andpropylene oxide, ethylene oxide addition polymers of poly(propyleneoxide) glycol, and copolymer glycols of ethylene oxide andtetrahydrofuran. Examples of aliphatic polyesters includepoly(E-caprolactone), polyenantholactone, polycaprolactone, polybutyleneadipate and polyethylene adipate.

In this invention, from the standpoint of the elastic properties,suitable use can be made of poly(tetramethylene oxide) glycol, ethyleneoxide adducts of poly(propylene oxide)glycol, copolymer glycols ofethylene oxide and tetrahydrofuran, poly(E-caprolactone), polybutyleneadipate and polyethylene adipate. Of these, the use of, in particular,poly(tetramethylene oxide)glycol, ethylene oxide adducts ofpoly(propylene oxide)glycol and copolymer glycols of ethylene oxide andtetrahydrofuran is recommended. The number-average molecular weight ofthese segments in the copolymerized state is preferably from about 300to about 6,000.

Component (III-a) can be produced by a known method. Specifically, usecan be made of, for example, the method of carrying out atransesterification reaction on a lower alcohol diester of adicarboxylic acid, an excess amount of a low-molecular-weight glycol anda low-melting polymer segment component in the presence of a catalystand polycondensing the resulting reaction product, or the method ofcarrying out an esterification reaction on a dicarboxylic acid, anexcess amount of glycol and a low-melting polymer segment component inthe presence of a catalyst and polycondensing the resulting reactionproduct.

The proportion of component (III-a) accounted for by component (III-a2)is from 30 to 60 wt %. The preferred lower limit in this case can be setto 35 wt % or more, and the preferred upper limit can be set to 55 wt %or less. When the proportion of component (III-a2) is too low, theimpact resistance (especially at low temperatures) and the compatibilitymay be inadequate. On the other hand, when the proportion of component(III-a2) is too high, the rigidity of the resin composition (and themolded body) may be inadequate.

The rigid resin serving as component (III-b) is not particularlylimited. For example, one or more selected from the group consisting ofpolycarbonates, acrylic resins, styrene resins such as ABS resins andpolystyrenes, polyester resins, polyamide resins, polyvinyl chloridesand modified polyphenylene ethers may be used. In this invention, fromthe standpoint of compatibility, a polyester resin may be preferablyused. More preferably, the use of polybutylene terephthalate and/orpolybutylene naphthalate is recommended.

Component (III-a) and component (III-b) are blended in a ratio,expressed as (III-a): (III-b), which is not particularly limited,although this ratio by weight is preferably set to from 50:50 to 90:10,and more preferably from 55:45 to 80:20. When the proportion ofcomponent (III-a) is too low, the low-temperature impact resistance maybe inadequate. On the other hand, when the proportion of (III-a) is toohigh, the rigidity of the composition (and the molded body), as well asthe molding processability, may be inadequate.

A commercial product may be used as the thermoplastic polyesterelastomer (III). Specific examples include those available as Hytrel®from DuPont-Toray Co. Ltd.

Component (III) has a material hardness on the Shore D hardness scalewhich, to enhance the spin rate on approach shots, is preferably 45 orless, more preferably 43 or less, and even more preferably 41 or less.The lower limit is a Shore D hardness of preferably at least 36, andmore preferably at least 38.

Component (III) has a rebound resilience which, to lower the initialvelocity on approach shots, is preferably 74% or less, more preferably73% or less, and even more preferably 72% or less. The lower limit ofthis rebound resilience is preferably at least 50%, more preferably atleast 52%, and even more preferably at least 60%. The rebound resilienceis measured in accordance with JIS-K 6255: 2013.

The thermoplastic polyester elastomer serving as component (III) has amelt viscosity of 1.5×10⁴ dPa·s or less, preferably 1.45×10⁴ dPa·s orless, more preferably 1.0×10⁴ dPa·s or less, and even more preferably0.8×10⁴ dPa·s or less. The lower limit is preferably at least 0.4×10⁴dPa·s, and more preferably at least 0.5×10⁴ dPa·s. With this meltviscosity, hardenability after molding of the resin composition isimparted and a good moldability (productivity) can be maintained. Thismelt viscosity indicates the value measured with a Capilograph (a typeof capillary rheometer) at a temperature of 200° C. and a shear rate of243 sec⁻¹ in accordance with ISO 11443: 1995.

The amount of component (III) included per 100 parts by weight ofcomponent (I) is 20 parts by weight or less, and preferably 15 parts byweight or less. At above this value, a decrease in the scuff resistancemay occur. The lower limit in the amount of component (III) included per100 parts by weight of component (I) is preferably at least 3 parts byweight, and more preferably at least 5 parts by weight.

In addition to the above resin components, other resin materials may beincluded in the resin composition containing components (I) to (III).The purposes for doing so are, for example, to further improve theflowability of the golf ball resin composition and to enhance such ballproperties as the rebound and the durability to cracking.

Specific examples of other resin materials that may be used includepolyamide elastomers, ionomer resins,ethylene-ethylene/butylene-ethylene block copolymers and modified formsthereof, polyacetals, polyethylenes, nylon resins, methacrylic resins,polyvinyl chlorides, polycarbonates, polyphenylene ethers, polyarylates,polysulfones, polyethersulfones, polyetherimides and polyamideimides.These may be used singly or two or more may be used together.

In addition, an active isocyanate compound may be included in the aboveresin composition. This active isocyanate compound reacts with thepolyurethane or polyurea serving as the base resin, enabling the scuffresistance of the overall resin composition to be further enhanced.Moreover, the isocyanate has a plasticizing effect which increases theflowability of the resin composition, enabling the moldability to beimproved.

Any isocyanate compound employed in ordinary polyurethanes may be usedwithout particular limitation as the above isocyanate compound. Forexample, aromatic isocyanate compounds that may be used include2,4-toluene diisocyanate, 2,6-toluene diisocyanate and mixtures of both,4,4-diphenylmethane diisocyanate, m-phenylene diisocyanate and4,4′-biphenyl diisocyanate. Use can also be made of the hydrogenatedforms of these aromatic isocyanate compounds, such asdicyclohexylmethane diisocyanate. Other isocyanate compounds that may beused include aliphatic diisocyanates such as tetramethylenediisocyanate, hexamethylene diisocyanate (HDI) and octamethylenediisocyanate; and alicyclic diisocyanates such as xylene diisocyanate.Further examples of isocyanate compounds that may be used includeblocked isocyanate compounds obtained by reacting the isocyanate groupson a compound having two or more isocyanate groups on the ends with acompound having active hydrogens, and uretdiones obtained by thedimerization of isocyanate.

The amount of the above isocyanate compounds included per 100 parts byweight of the polyurethane or polyurea serving as the base resin ispreferably at least 0.1 part by weight, and more preferably at least 0.5part by weight. The upper limit is preferably not more than 30 parts byweight, and more preferably not more than 20 parts by weight. When toolittle is included, a sufficient crosslinking reaction may not beobtained and an improvement in the properties may not be observable. Onthe other hand, when too much is included, discoloration over time dueto heat and ultraviolet light may increase, or problems such as a lossof thermoplasticity or a decline in resilience may arise.

In addition, optional additives may be suitably included in the aboveresin composition according to the intended use thereof. Examples ofoptional additives include inorganic fillers, organic staple fibers,reinforcing agents, crosslinking agents, pigments, dispersants,antioxidants, ultraviolet absorbers and light stabilizers. When suchadditives are included, the amount thereof per 100 parts by weight ofthe base resin is preferably at least 0.1 part by weight, and morepreferably at least 0.5 part by weight, but preferably not more than 10parts by weight, and more preferably not more than 4 parts by weight.

The resin composition has a rebound resilience measured in accordancewith JIS-K 6255: 2013 which, in order to increase the spin rate onapproach shots, is preferably at least 50%, more preferably at least52%, and even more preferably at least 54%. The upper limit ispreferably 72% or less, more preferably 70% or less, and even morepreferably 68% or less.

The resin composition has a material hardness on the Shore D hardnessscale which, in order to increase the spin rate on approach shots, ispreferably 49 or less, more preferably 48 or less, and even morepreferably 47 or less. From the standpoint of moldability, the lowerlimit in the material hardness on the Shore D hardness scale ispreferably at least 30, and more preferably at least 35.

The resin composition may be prepared by mixing together the ingredientsusing any of various types of mixers, such as a kneading-typesingle-screw or twin-screw extruder, a Banbury mixer, a kneader or aLabo Plastomill. Alternatively, the ingredients may be mixed together bydry blending at the time that the resin composition is to beinjection-molded. In addition, when an active isocyanate compound isused, it may be incorporated at the time of resin mixture using varioustypes of mixers, or a resin masterbatch already containing the activeisocyanate compound and other ingredients may be separately prepared andthe various components mixed together by dry blending at the time thatthe resin composition is to be injection-molded.

The method of molding the cover from the above resin composition mayinvolve, for example, feeding the resin composition into an injectionmolding machine and molding the cover by injecting the molten resincomposition over the core. In this case, the molding temperature differsaccording to the type of polyurethane or polyurea (I) serving as thebase resin, but is typically in the range of 150 to 270° C.

The cover has a thickness of preferably at least 0.4 mm, more preferablyat least 0.5 mm, and even more preferably at least 0.6 mm. The upperlimit is preferably not more than 3.0 mm, and more preferably not morethan 2.0 mm.

In cases where an intermediate layer is interposed between the abovecore and the above cover, it is preferable to employ any of varioustypes of thermoplastic resins used in golf ball cover materials,especially an ionomer resin, as the intermediate layer material. Acommercial product may be used as the ionomer resin. In this case, thethickness of the intermediate layer may be set within a range similar tothat for the thickness of the cover described above.

In the golf ball of the invention, for reasons having to do with theaerodynamic performance, numerous dimples are provided on the surface ofthe outermost layer. The number of dimples formed on the surface of theoutermost layer is not particularly limited. However, to enhance theaerodynamic performance and increase the distance traveled by the ball,this number is preferably at least 250, more preferably at least 270,even more preferably at least 290, and most preferably at least 300. Theupper limit is preferably not more than 400, more preferably not morethan 380, and even more preferably not more than 360.

In the present invention, a coating layer is formed on the surface ofthe cover. This coating layer is formed of a urethane coating thatincludes an organic solvent having a boiling point of 80° C. or less anda silicone-based additive. It is preferable to use as the urethanecoating a two-part curable urethane coating, specifically one thatincludes a base resin composed primarily of a polyol resin and a curingagent composed primarily of a polyisocyanate.

The polyol is not particularly limited, although one, two or morepolyester polyols may be suitably used as the polyol. For example, twotypes of polyester polyol, designated here as Polyester Polyol A (orComponent A) and Polyester Polyol B (or Component B), may be used as thebase resin. These two types of polyester polyol have differingweight-average molecular weights (Mw), the weight-average molecularweight of

Component A being from 20,000 to 30,000, and the weight-averagemolecular weight of Component B being from 800 to 1,500. Theweight-average molecular weight of Component A is more preferably from22,000 to 29,000, and even more preferably from 23,000 to 28,000. Theweight-average molecular weight of Component B is more preferably from900 to 1,200, and even more preferably from 1,0000 to 1,100.

The two types of polyester polyol can each be obtained by thepolycondensation of a polyol with a polybasic acid. Examples of thepolyol include diols such as ethylene glycol, 1,2-propanediol,1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol,neopentyl glycol, diethylene glycol, dipropylene glycol, hexyleneglycol, dimethylolheptane, polyethylene glycol and polypropylene glycol;and triol, tetraol, and polyols having an alicyclic structure. Examplesof the polybasic acid include aliphatic dicarboxylic acids such assuccinic acid, adipic acid, sebacic acid, azelaic acid and dimer acid;aliphatic unsaturated dicarboxylic acids such as fumaric acid, maleicacid, itaconic acid and citraconic acid; aromatic polycarboxylic acidssuch as phthalic acid, isophthalic acid, terephthalic acid, trimelliticacid and pyromellitic acid; dicarboxylic acids having an alicyclicstructure, such as tetrahydrophthalic acid, hexahydrophthalic acid,1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid andendomethylenetetrahydrophthalic acid; andtris-2-carboxyethylisocyanurate. In particular, a polyester polyol inwhich a cyclic structure has been introduced onto the resin skeleton maybe used as the polyester polyol serving as Component A. Examples includepolyester polyols obtained by the polycondensation of a polyol having analicyclic structure, such as cyclohexane dimethanol, with a polybasicacid; and polyester polyols obtained by the polycondensation of a polyolhaving an alicyclic structure with a diol or triol and a polybasic acid.A polyester polyol having a hyperbranched structure may be used as thepolyester polyol serving as Component B. Examples include polyesterpolyols having a branched structure, such as NIPPOLAN 800 from TosohCorporation.

The weight-average molecular weight (Mw) of the overall base resincomposed of the above two types of polyester polyol is preferably from13,000 to 23,000, and more preferably form 15,000 to 22,000. Thenumber-average molecular weight (Mn) of the overall base resin composedof the above two types of polyester polyol is preferably from 1,100 to2,000, and more preferably from 1,300 to 1,850. When these averagemolecular weights (Mw and Mn) fall outside of the above ranges, the wearresistance of the applied film (coat) may decrease. The weight-averagemolecular weight and the number-average molecular weight are measuredvalues (polystyrene-equivalent values) obtained by gel permeationchromatography (GPC) measurement with differential refractometerdetection. The contents of the above Polyester Polyols A and B are notparticularly limited, although it is preferable for the Component Acontent to be from 20 to 30 wt % of the total amount of base resin andthe Component B content to be from 2 to 18 wt % of the overall baseresin.

In cases where only one type of polyester polyol is used as the polyol,the use of Polyester Polyol A is preferred.

The polyisocyanate includes two types of compound: an isocyanurate andan adduct of hexamethylene diisocyanate. Generally, isocyanateprepolymers are divided into three types of structures: adducts,biurets, and isocyanurates. As used herein, “adduct” refers to anaddition product of a diisocyanate and trimethylolpropane, and“isocyanurate” refers to a diisocyanate trimer.

The above hexamethylene diisocyanate also includes modified formsthereof.

Examples of modified hexamethylene diisocyanates includepolyester-modified hexamethylene diisocyanate and urethane-modifiedhexamethylene diisocyanate.

To increase the spin rate of the golf ball on approach shots, the mixingratio by weight (A)/(B) between the hexamethylene diisocyanateisocyanurate (A) and the hexamethylene diisocyanate adduct (B) ispreferably from 85/15 to 15/85, more preferably from 80/20 to 20/80, andeven more preferably from 75/25 to 25/75.

Examples of hexamethylene diisocyanate (HMDI) isocyanurates includethose available under the tradenames Coronate® 2357 (Tosoh Corporation),Sumidur N3300 (Sumika Covestro Urethane Co., Ltd.), Duranate™ TPA-100(Asahi Kasei Corporation), Takenate™ D170N and Takenate™ D177N (bothfrom Mitsui Chemicals, Inc.), and Burnock DN-980 (DIC Corporation).These may be used singly or two or more may be used in combination.

Examples of hexamethylene diisocyanate (HMDI) adducts include thoseavailable under the trade names Coronate® HL (Tosoh Corporation),Takenate™ D160N (Mitsui Chemicals, Inc.), Duranate™ E402-80B andDuranate™ E405-70B (both from Asahi Kasei Corporation), and BurnockDN-955 and Burnock DN-955S (both from DIC Corporation). These may beused singly or two or more may be used in combination.

The molar ratio between hydroxyl groups (OH groups) on the polyesterpolyol and isocyanate groups (NCO groups) on the polyisocyanate,expressed as NCO/OH, is preferably at least 0.6, and more preferably atleast 0.65. The upper limit is preferably not more than 1.5, morepreferably not more than 1.0, and even more preferably not more than0.9. When this molar ratio is less than 0.6, unreacted hydroxyl groupsremain and the performance and water resistance as a golf ball coat mayworsen. On the other hand, at above 1.5, the large excess of isocyanategroups may react with moisture to form fragile urea bonds, as a resultof which the performance as a golf ball coat may decline.

An amine catalyst or an organometallic catalyst may be used as thecuring catalyst (organometallic compound). A metallic soap of aluminum,nickel, zinc, tin or the like that has hitherto been included as acuring agent for two-part curable urethane coatings may be suitably usedas this organometallic compound.

In this invention, a silicone-based additive such as a silicone resin,silicone fluid or silicone rubber is included in the coating compositionin order to lower the coefficient of friction at the golf ball surfaceand impart water repellency. A silicone-modified acrylate can be used asthe silicone resin. As used herein, “silicone-modified acrylate” refersto a surface conditioner in which an acrylic structure and a siliconestructure have been incorporated onto one molecule. Because apolysiloxane chain is attached to the acrylic skeleton, unlike ordinarypolyrotaxane-type silicone resins, slip does not readily occur even whenthe amount of silicone-based additive included is increased, enablingthe water-repellency to be enhanced. Examples of silicone-modifiedacrylates include those available under the trade names BYK-3550 andBYK-3700 (both from BYK-Chemie GmbH). Exemplary silicone fluids includemethyl hydrogen silicone fluids and dimethyl silicone fluids.

To lower the coefficient of friction at the golf ball surface and impartsufficient water repellency, the silicone-based additive is included ina proportion relative to the overall coating composition that ispreferably at least 0.01 wt %, more preferably at least 0.02 wt %, andeven more preferably at least 0.03 wt %. The upper limit is preferablynot more than 0.5 wt %. When this upper limit is exceeded, the desiredcontrollability on approach shots may not be obtained.

Known compounding ingredients for coatings may be optionally included inthe coating composition. For example, thickeners, ultraviolet absorbers,fluorescent brighteners, slip agents and pigments may be suitablyincluded.

When the coating composition is used, a coating layer can be formed onthe ball surface by first preparing the coating composition at the timeof application, applying the composition onto the ball surface by anordinary coating operation and then passing through a drying step.Although not particularly limited, preferred use can be made of spraypainting, electrostatic painting or dipping as the method ofapplication.

Various organic solvents may be mixed into the coating composition.Examples of such organic solvents include aromatic solvents such astoluene, xylene and ethylbenzene; ester solvents such as ethyl acetate,butyl acetate, propylene glycol methyl ether acetate and propyleneglycol methyl ether propionate; ketone solvents such as acetone, methylethyl ketone, methyl isobutyl ketone and cyclohexanone; ether solventssuch as diethylene glycol dimethyl ether, diethylene glycol diethylether and dipropylene glycol dimethyl ether; alicyclic hydrocarbonsolvents such as cyclohexane, methyl cyclohexane and ethyl cyclohexane;and petroleum hydrocarbon-based solvents such as mineral spirits.

In this invention, an organic solvent having a boiling point of 80° C.or less is included in the coating composition. The purpose is tominimize the silicone component that rises to the surface duringcoating. Examples of suitable organic solvents having a boiling point of80° C. or less include hydrocarbon solvents such as n-hexane (68° C.),cyclohexane (80° C.) and benzene (80° C.); ester solvents such as methylacetate (57° C.) and ethyl acetate (77° C.); and ketone solvents such asacetone (56° C.) and methyl ethyl ketone (79° C.). The numbers withinparentheses here indicate boiling points. Of these organic solventshaving a boiling point of 80° C. or less, taking into consideration theeffects of the solvent on the body and the environment, the use of estersolvents and ketone solvents is preferred.

The above organic solvent having a boiling point of 80° C. or less isincluded in a proportion, based on the overall amount of the coatingcomposition, which, in order to fully ensure the effect of minimizingthe silicone component that rises to the surface during coating, ispreferably at least 20 wt %, more preferably at least 30 wt %, and evenmore preferably at least 40 wt %. The upper limit is preferably 80 wt %or less. Above this upper limit, good leveling of the coating layersurface may not occur and the gloss of the coated surface may decrease.

The drying step may be similar to that used for known two-part curableurethane coatings, with the drying temperature typically being set to atleast about 40° C., especially between 40° C. and 60° C., and the dryingtime typically being set to from 20 to 90 minutes, especially from 40 to50 minutes.

The thickness of the coating layer, although not particularly limited,is preferably from 3 to 50 μm, and more preferably from 5 to 20 μm.

In the golf ball of the invention having the above coating layer, theball has a deflection when compressed under a final load of 1,275 N (130kgf) from an initial load of 98 N (10 kgf) of preferably at least 2.0mm, more preferably at least 2.3 mm, and even more preferably at least2.5 mm. The upper limit is preferably 3.3 mm or less, and morepreferably 3.0 mm or less. When this value is too small, there is apossibility that the spin rate on shots with a driver will rise,resulting in a decreased distance. On the other hand, when this value istoo large, the spin rate on approach shots may decrease, resulting inlower controllability.

Also, in the golf ball of the invention having the above coating layer,when the ball is allowed to fall freely onto an impact surface inclined58° to the horizontal from a height position 3 m above the surface, theamount of sliding by the ball, designated as “Ds” and defined as theperpendicular displacement by the ball from where sliding of the ball onthe impact surface begins to where sliding ends, is 2.0 mm or less, morepreferably 1.5 mm or less, and even more preferably 1.2 mm or less.Within this range in values, the golfer has a sensation of the ball“clinging” to the clubface, giving the golf ball a good feel at impact.The sensation of the ball “clinging” to the clubface presumably refersto the phenomenon where, when the golfer hits a golf ball and the faceof the golf club and the ball collide, the golf ball does not slide muchalong the surface of the clubface. The numerical value of theabove-described sliding amount (Ds) is used as the metric for thissensory evaluation. For a more thorough explanation, reference can bemade to paragraph [0043] and FIG. 3 of JP-A 2019-217078, a prior-artdisclosure filed by the present applicant.

Moreover, in this golf ball, the contact time of the ball after sliding,designated as “Tc” and defined as the time from when sliding of the ballon the impact surface ends until the ball separates from the impactsurface, is at least 400 μs, more preferably at least 500 μs, and evenmore preferably at least 540 μs. Within this range in values, the golferhas a sensation of the ball “riding” on the clubface, giving the golfball a good feel at impact. The sensation of the ball “riding” on theclubface presumably refers to the phenomenon where, when the golfer hitsa golf ball and the face of the golf club and the ball collide, the golfball comes into prolonged contact with the clubface. The numerical valueof the above-described sliding amount (Tc) is used as the metric forthis sensory evaluation. For a more thorough explanation, reference canbe made to paragraph [0048] and FIGS. 3 and 4 of JP-A 2019-217078, aprior-art disclosure filed by the present applicant. The above contacttime after sliding (Tc) corresponds to the “second contact time” in JP-A2019-217078.

The golf ball of the invention can be made to conform to the Rules ofGolf for play. The inventive ball may be formed to a diameter which issuch that the ball does not pass through a ring having an inner diameterof 42.672 mm and is not more than 42.80 mm, and to a weight which ispreferably between 45.0 and 45.93 g.

EXAMPLES

The following Examples and Comparative Examples are provided toillustrate the invention, and are not intended to limit the scopethereof

Examples 1 to 8, Comparative Examples 1 to 6

A 38.6 mm core is formed in each Example. The core formulation, which iscommon to all the Examples of the invention and the ComparativeExamples, includes as the base rubber 20 parts by weight ofPolybutadiene A (available under the trade name BR51 from JSRCorporation) and 80 parts by weight of Polybutadiene B (available underthe trade name BR 730 from JSR Corporation), 29.5 parts by weight ofzinc acrylate (Wako Pure Chemical Industries, Ltd.), 0.6 part by weightof dicumyl peroxide (available under the trade name Percumyl D from NOFCorporation) as an organic peroxide, 0.1 part by weight of2,2-methylenebis(4-methyl-6-butylphenol) (available under the trade nameNocrac NS-6 from Ouchi Shinko Chemical Industry Co., Ltd.) as anantioxidant, 19.3 parts by weight of zinc oxide (available under thetrade name Zinc Oxide Grade 3 from Sakai Chemical Co., Ltd.) and 0.3part by weight of the zinc salt of pentachlorothiophenol (Wako PureChemical Industries, Ltd.) as an organosulfur compound. Vulcanization ofthe rubber composition is carried out at a temperature of 155° C. for aperiod of 15 minutes. The specific gravity of the composition is 1.138.

Formation of the Intermediate Layer

Next, an intermediate layer-forming resin material is injection-moldedover the 38.6 mm diameter core, thereby producing an intermediatelayer-encased sphere having a 1.25 mm thick intermediate layer. Theresin material in the intermediate layer, which is common to all of theExamples and Comparative Examples, includes Himilan 1605, Himilan 1557and Himilan 1706 (all trade names for ionomer resins available fromDow-Mitsui Polychemicals Co., Ltd.) in a weight ratio of 50:12:38. Inaddition, 1.1 parts by weight of trimethylolpropane (Tokyo ChemicalIndustry Co., Ltd.) is included per 100 parts by weight of the totalamount of this ionomer resin.,

Formation of Cover (Outermost Layer)

Next, using a different injection mold, the cover (outermostlayer)-forming resin material shown in Table 1 below is injection-moldedover the above intermediate layer-encased sphere, thereby producing a42.7 mm diameter three-piece golf ball having an outermost layer with athickness of 0.8 mm

Details on the ingredients included in the cover materials in Table 1are as follows.

-   -   TPU 1: An ether-type thermoplastic polyurethane available from        DIC Covestro Polymer, Ltd. under the trade name “Pandex” (Shore        D hardness, 43; rebound resilience, 61%)    -   TPU 2: An ether-type thermoplastic polyurethane available from        DIC Covestro Polymer, Ltd. under the trade name “Pandex” (Shore        D hardness, 47; rebound resilience, 54%)    -   S.O.E. 51611: A hydrogenated aromatic vinyl-based elastomer        available from Asahi Kasei Corporation (styrene content, 60 wt        %; Shore D hardness, 23; rebound resilience, 20%)    -   Hytrel 2401: A thermoplastic polyether ester elastomer available        from DuPont-Toray Co., Ltd. (Shore D hardness, 40; rebound        resilience, 67%; melt viscosity, 5,700 dPa·s)

Material Hardness of Cover

The resin material is molded into sheets having a thickness of 2 mm andleft to stand for two weeks at a temperature of 23±2° C. At the time ofmeasurement, three sheets are stacked together and the Shore D hardnessis measured with a Shore D durometer in accordance with ASTM D2240. TheP2 Automatic Rubber Hardness Tester from Kobunshi Keiki Co., Ltd. with aShore D durometer mounted thereon is used for measuring the hardness.The maximum value is read off as the hardness value.

Formation of Coating Layer (Coat)

Next, in each Example, the coating composition made up of the baseresins and curing agents in the coating formulation shown in Table 1below is applied with an air spray gun onto the surface of the cover(outermost layer) having numerous dimples formed thereon, producing agolf ball with a 15 μm thick coating layer (coat) on top.

Base Resin

A polyester polyol synthesized by the following method is used as thepolyol of the base resin.

A reactor equipped with a reflux condenser, a dropping funnel, a gasinlet and a thermometer is charged with 140 parts by weight oftrimethylolpropane, 95 parts by weight of ethylene glycol, 157 parts byweight of adipic acid and 58 parts by weight of1,4-cyclohexanedimethanol, following which the reaction is effected byraising the temperature to between 200 and 240° C. under stirring andheating for 5 hours. This yields a polyester polyol having an acid valueof 4, a hydroxyl value of 170 and a weight-average molecular weight (Mw)of 28,000.

Aside from Comparative Examples 3, 5 and 6, ethyl acetate (boilingpoint, 77° C.) is used in the specific amount shown in Table 1 as theorganic solvent included in the base resin. In Comparative Examples 3, 5and 6, butyl acetate (boiling point, 126° C.) is used in the specificamount shown in Table 1. In Examples 1 to 8 and Comparative Examples 3,5 and 6, a silicone-modified acrylate (available under the trade nameBYK-3700 from BYK-Chemie GmbH) is included in the specific amount shownin Table 1 as the silicone-based additive in the base resin.

Curing Agent

An isocyanate of hexamethylene diisocyanate (HMDI) available under theproduct name Duranate™ TPA-100 from Asahi Kasei Corporation (NCOcontent, 23.1%; nonvolatiles, 100%) is used as the Curing Agent Aisocyanate. An adduct of hexamethylene diisocyanate (HMDI) availableunder the product name Duranate™ E402-80B from Asahi Kasei Corporation(NCO content, 7.6%; nonvolatiles, 80%) is used as the Curing Agent Bisocyanate.

In all of the Examples, butyl acetate (boiling point, 126° C.) is usedin the specific amount shown in Table 1 as the organic solvent in thecuring agent.

The ball deformation, static coefficient of friction, feel at impact andcontrollability on approach shots of the golf balls obtained in therespective Examples are evaluated. Those results are shown in Table 1.

Ball Deformation

The ball is placed on a hard plate and the amount of deflection whencompressed under a final load of 1,275 N (130 kgf) from an initial loadof 98 N (10 kgf) is measured. The deflection is a value measured afterholding the ball isothermally at a temperature of 23.9° C.

Static Coefficient of Friction

The golf ball is mounted on a jig and the static coefficient of frictionof the golf ball when pulled under the following conditions is measured.

Measurement Conditions

-   -   Normal force: 3.5N    -   Face plate: stainless steel    -   Pull rate: 50 mm/min    -   Temperature: 23° C.

Feel at Impact

A sand wedge (X-WEDGE H8101, from Bridgestone Sports Co., Ltd.; 58°) ismounted on a golf swing robot and the feel at impact of a golf ball hitat a head speed of 20 m/s is evaluated using the amount of sliding bythe ball Ds (mm) when struck and the contact time after sliding Tc (μs)as the metrics.

Test Method

An evaluation system like that in FIG. 1 of JP-A 2019-217078 isfurnished. That is, as shown in FIG. 1 of this published application,the evaluation system has a high-speed camera, an evaluation apparatusand a collision member.

-   -   Step 1: The golf ball is allowed to fall freely from a height of        3 m.    -   Step 2: The golf ball is made to strike an impact surface        inclined 58° to the horizontal.    -   Step 3: The state of the golf ball on the impact surface is        observed with a high-speed camera, and the amount of sliding        Ds (mm) by the golf ball and the contact time after sliding Tc        (p,$) are analyzed and computed.

Evaluation of “Clinging” Sensation

-   -   Excellent (Exc): Amount of sliding (Ds) is 1.30 mm or less    -   Good: Amount of sliding (Ds) is in the range of 1.31 to 2.00 mm    -   NG: Amount of sliding (Ds) is 2.01 mm or more

Evaluation of “Riding” Sensation

-   -   Excellent (Exc): Amount of contact after sliding (Tc) is at        least 540 μs    -   Good: Amount of contact after sliding (Tc) is from 500 to 539 μs    -   NG: Amount of contact after sliding (Tc) is 499 μs or less

Controllability on Approach Shots (under normal dry conditions)

A sand wedge (X-WEDGE H8101, from Bridgestone Sports Co., Ltd.; 58°) ismounted on a golf swing robot and the initial velocity (m/s) andbackspin rate (rpm) of a golf ball hit at a head speed of 20 m/s aremeasured. Determinations of the controllability are carried out bysensory evaluations. The clubs used are the respective golfers' own sandwedges (SW). The golfers use the following criteria to evaluate thecontrollability on actual shots.

-   -   Excellent (Exc): Controllability is excellent.    -   Good: Controllability is good.    -   NG: Controllability is poor.

A determination as to whether the controllability is good or not isbased not only on the ball spin rate, but also on the length of thecontact time between the ball and the clubface owing to the initialvelocity of the ball.

Controllability on Approach Shots (under Wet Conditions)

In addition, to ascertain the water-repelling effects, the spin rate ofthe golf ball on approach shots when the ball is wet is evaluated underthe following conditions.

The golf ball is immersed in a water-filled bucket, the backspin rate(rpm) of the ball when struck while drops of water still adhere to theball is measured, and a determination is made based on the followingcriteria.

-   -   Excellent (Exc): 5,750 rpm or more    -   Good: from 5,000 to 5,749 rpm    -   NG: 4,999 or less

TABLE 1 Example 1 2 3 4 5 6 7 8 Core common to all Examples Intermediatelayer common to all Examples Cover Component TPU 1 100 100 100 100 100100 100 formulation (I) TPU 2 100 (pbw) Component S.O.E. S1611 5 10 15 5(II) Component Hytrel 2401 14.5 14.5 14.5 14.5 14.5 14.5 14.5 14.5 (III)Material hardness of cover 43 43 43 43 43 43 43 47 (Shore D) CoatingBase resin Polyol 30 30 30 30 30 30 30 30 formulation Butyl acetate(pbw) (solvent) Ethyl acetate 70 70 70 70 70 70 70 70 (solvent)Silicone-based 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 additive Curingagent Curing Agent A 18 16 10 4 16 16 16 16 (isocyanurate) Curing AgentB 2 4 10 16 4 4 4 4 (adduct) Butyl acetate 30 30 30 30 30 30 30 30(solvent) Ratio of solvent 47 47 47 47 47 47 47 47 that boils at 80° C.or less (%) Ball Deformation (mm) 2.64 2.64 2.64 2.64 2.64 2.64 2.642.56 Static coefficient of friction 0.40 0.46 0.50 0.53 0.46 0.46 0.460.46 Evaluations Feel at impact Amount of 1.43 1.35 1.30 1.29 1.13 1.351.52 2.05 sliding Ds (mm) “Clinging” good good Exc Exc Exc good good NGsensation Contact time Tc 507 533 543 548 562 548 530 406 (μs) “Riding”good good Exc Exc Exc Exc good NG sensation Controllability Initialvelocity 16.11 16.12 16.12 16.14 16.07 16.06 16.05 15.99 on approach(m/s) shots Spin rate (rpm) 6,803 6,835 6,843 6,893 6,860 6,842 6,8526,775 Rating good good good Exc Exc Exc Exc good Wet spin rate 5,5806,024 5,863 6,320 5,790 5,830 5,840 6,030 (rpm) Rating good Exc Exc ExcExc Exc Exc Exc Comparative Example 1 2 3 4 5 6 Core common to allExamples Intermediate layer common to all Examples Cover Component TPU 1100 100 100 100 100 100 formulation (I) TPU 2 (pbw) Component S.O.E.S1611 5 5 15 (II) Component Hytrel 2401 14.5 14.5 14.5 14.5 14.5 14.5(III) Material hardness of cover 43 43 43 43 43 43 (Shore D) CoatingBase resin Polyol 30 30 30 30 30 30 formulation Butyl acetate 70 70 70(pbw) (solvent) Ethyl acetate 70 70 70 (solvent) Silicone-based 0.050.05 0.05 additive Curing agent Curing Agent A 20 16 16 16 16 16(isocyanurate) Curing Agent B 4 4 4 4 4 (adduct) Butyl acetate 30 30 3030 30 30 (solvent) Ratio of solvent 47 47 0 47 0 0 that boils at 80° C.or less (%) Ball Deformation (mm) 2.64 2.64 2.64 2.64 2.64 2.64 Staticcoefficient of friction 0.40 0.52 0.35 0.52 0.35 0.35 Evaluations Feelat impact Amount of 1.44 1.35 1.53 0.96 1.68 1.62 sliding Ds (mm)“Clinging” good good good Exc good good sensation Contact time Tc 467510 453 594 488 503 (μs) “Riding” NG good NG Exc NG good sensationControllability Initial velocity 16.12 16.13 16.03 16.09 16.07 16.1 onapproach (m/s) shots Spin rate (rpm) 6,834 6,860 6,699 6,810 6,669 6,611Rating good Exc NG Exc NG NG Wet spin rate 2,950 3,154 5,730 3,047 6,2406,020 (rpm) Rating NG NG good NG Exc Exc

Referring to Table 1, in Examples 1 to 4, the coating includes asilicone-based additive, the curing agent includes an adduct of HMDI,and the results indicate a good controllability on approach shots (bothunder normal dry conditions and when wet). In Examples 5 to 7, the coverincludes a urethane, a polyester and an aromatic vinyl elastomer, andthe results indicate a good controllability compared with Example 2.

By contrast, in Comparative Example 1, because the coating does notinclude a silicone-based additive and the curing agent does not includean adduct of HMDI, the spin rate of the ball when wet is low.

In Comparative Example 2, because the coating does not include asilicone-based additive, the spin rate of the ball when wet is low.

In Comparative Example 3, because the coating does not include anorganic solvent having a boiling point of 80° C. or less, the staticcoefficient of friction is small and the spin rate is low.

In Comparative Example 4, because the coating does not include asilicone-based additive, the spin rate of the ball when wet is low.

In Comparative Example 5, because the coating does not include anorganic solvent having a boiling point of 80° C. or less, the staticcoefficient of friction is small and the spin rate is low.

In Comparative Example 6, because the coating does not include anorganic solvent having a boiling point of 80° C. or less, the staticcoefficient of friction is small and the spin rate is low.

-   Japanese Patent Application No. 2021-102359 is incorporated herein    by reference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A golf ball comprising a core, a cover and a coating layer, whereinthe coating layer is formed of a urethane coating comprised of anorganic solvent having a boiling point of 80° C. or less, asilicone-based additive and, as a curing agent, a polyisocyanate whichincludes an adduct and an isocyanurate of hexamethylene diisocyanate(HMDI).
 2. The golf ball of claim 1, wherein the organic solvent havinga boiling point of 80° C. or less is included in a proportion, based onthe overall amount of the coating composition, of at least 20 wt %. 3.The golf ball of claim 1, wherein the mixing ratio by weight (A)/(B)between the isocyanurate (A) and the adduct (B) of hexamethylenediisocyanate is from 85/15 to 15/85.
 4. The golf ball of claim 1,wherein at least one layer of the cover is formed of a resin compositioncomprising: (I) a polyurethane or a polyurea, and (II) an aromatic vinylelastomer, which aromatic vinyl elastomer has a Shore D hardness of 30or less and a rebound resilience of 30% or less.
 5. The golf ball ofclaim 4, wherein the content of component (II) is from 5 to 20 parts byweight per 100 parts by weight of component (I).
 6. The golf ball ofclaim 4, wherein the resin composition further comprises (III) athermoplastic polyester elastomer having a Shore D hardness of 45 orless, a rebound resilience of 74% or less, and a melt viscosity at 200°C. and a shear rate of 243 sec⁻¹ of 1.5×10⁴ dPa·s or less.
 7. The golfball of claim 1 wherein, when the ball is allowed to fall freely onto animpact surface inclined 58° to the horizontal from a height position 3 mabove the surface, the amount of sliding by the ball, designated as “Ds”and defined as the perpendicular displacement by the ball from wheresliding of the ball on the impact surface begins to where sliding ends,is 2.0 mm or less, and the contact time of the ball after sliding,designated as “Tc” and defined as the time from when sliding of the ballon the impact surface ends until the ball separates from the impactsurface, is at least 400 μs.